Flowerday Callum E, Thalman Ryan, Asplund Matthew C, Badstubner Samuel A, Cook Adam K, Lundrigan Philip, Hansen Jaron C
Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States.
Department of Natural Science and Mathematics, Snow College, Ephraim, Utah 84627, United States.
Anal Chem. 2025 Jun 10;97(22):11831-11838. doi: 10.1021/acs.analchem.5c01515. Epub 2025 May 28.
Hydroxyl radical (OH) is the primary atmospheric oxidant, but it is challenging to measure due to its short half-life under atmospheric conditions (approximately 1 s) and low ambient concentrations (approximately 10 molecules/cm). While several measurement techniques exist, including laser-induced fluorescence with fluorescence assay by gas expansion (LIF-FAGE), differential optical absorption spectroscopy, and chemical ionization mass spectrometry (CIMS), often only LIF-FAGE and CIMS are considered available for field measurements. This study compares the performance of two instruments: a broadband cavity-enhanced absorption spectroscopy (BBCEAS) coupled with a CCD and a BBCEAS coupled with a Fabry-Pérot interferometer (BBCEAS-FP). The semiportable BBCEAS instrument benefits from spectroscopic specificity, avoiding interference from other species, and features inherent calibration, eliminating calibration errors. The effects of aerosols and turbulence on performance were also evaluated. A low-loss optic was used to measure the optical cavity reflectivity in an open-path configuration, and a butane flame served as the OH source during testing. The BBCEAS instrument achieved an extrapolated 1-h detection limit (1σ) of 1.5 × 10 molecules/cm for ambient-temperature OH. Applying a Gauss-Hermite filter reduced noise in the extinction spectrum by 2.66 times, lowering the extrapolated detection limit to 4.6 × 10 molecules/cm. The BBCEAS-FP, a more cost-effective and portable instrument, demonstrated a comparable extrapolated 1-h (1σ) detection limit of 1.5 × 10 molecules/cm.
羟基自由基（OH）是大气中的主要氧化剂，但由于其在大气条件下的半衰期较短（约1秒）且环境浓度较低（约10个分子/立方厘米），对其进行测量具有挑战性。虽然存在多种测量技术，包括激光诱导荧光结合气体膨胀荧光分析法（LIF-FAGE）、差分光学吸收光谱法和化学电离质谱法（CIMS），但通常只有LIF-FAGE和CIMS被认为可用于现场测量。本研究比较了两种仪器的性能：一种是与电荷耦合器件（CCD）联用的宽带腔增强吸收光谱仪（BBCEAS），另一种是与法布里-珀罗干涉仪联用的BBCEAS（BBCEAS-FP）。这种半便携式BBCEAS仪器具有光谱特异性，可避免其他物种的干扰，并且具有固有校准功能，可消除校准误差。还评估了气溶胶和湍流对性能的影响。在开放路径配置中使用低损耗光学器件测量光腔反射率，测试期间使用丁烷火焰作为OH源。对于环境温度下的OH，BBCEAS仪器实现了1.5×10个分子/立方厘米的外推1小时检测限（1σ）。应用高斯-厄米特滤波器使消光光谱中的噪声降低了2.66倍，将外推检测限降低至4.6×10个分子/立方厘米。更具成本效益且便携的BBCEAS-FP展示了相当的外推1小时（1σ）检测限，为1.5×10个分子/立方厘米。
